This invention relates to a value document such as a bank note, to a method for checking the presence of the same, and to a value-document system.
The authentication of value documents by means of luminescent substances has been known for some time. Use is preferably made of host lattices doped with rare earth metals, with the absorption ranges and emission regions being variable within a wide range through a suitable coordination of rare earth metal and host lattice. The employment of magnetic and electrically conductive materials for authentication is also per se known. Magnetism, electrical conductivity and luminescence emission are detectable by machine using commercially available measurement devices, while luminescence is also detectable visually when emission in the visible range is of sufficient intensity.
The problem of the authentication features of value documents being forged is practically as old as the authentication of the value documents. Anti-forgery security can be increased for example by employing not only one feature substance, but a plurality of feature substances in combination, for example a luminescent substance and a magnetic substance, or a luminescent substance and a substance influencing the luminescence properties. DE 10 2005 047 609 A1 describes feature substances for authentication of value documents that contain a luminescent substance and at least one further substance that is preferably magnetic or electrically conductive. The luminescent substance is present in particulate form and is surrounded by a shell formed from nanoparticles. The properties of the feature substance result from the interaction of the luminescence emission properties of the luminescent substance and the properties of the nanoparticles.